HVAC PRIME SOURCE, LLC

REFRIGERANTS

General

There is a wide variety of refrigerants used in air conditioning equipment depending on the application.
In general the most common refrigerants used in the industry belong to the following three categories -

  • CFC - These are the Chloro Fluoro Carbon refrigerants, such as R11, R12, R113, R114, etc. These
    refrigerants were identified as the most harmful to Ozone layer by the Montreal Protocol, and
    were phased out in 2000. However they are still being used in the older machines, with
    precautions to minimize release in accordance with EPA regulations. The most common application
    of these refrigerant is in the large centrifugal chillers. R12 was also used commonly in the older cars
    for air condition.
  • HCFC - These are the Hydro Chloro Fluoro Carbon refrigerants, such as R22, R123, etc. These
    refrigerants were identified as slightly harmful to the Ozone layer by Montreal Protocol, and will be
    completely phased out by 2030. See the EPA link below for the different stages of the phaseout.
    The R22 refrigerant is commonly used in reciprocating type of compressors, while R123 is used in
    centrifugal chillers as a temporary replacement for R11.
  • HFC - These are the Hydro Fluoro Carbon refrigerants, such as R134a. These are the new
    refrigerants that do not harm the Ozone layer, and are being used in the newer machines to
    replace the CFC and HCFC. R134a is now commonly used as a replacement of R12 and R500, and in
    all new cars air conditioning systems. R407c is used as a replacement for R22. One of the other
    common HFC used in new equipment now is R410a.

There is extensive research going on to identify new refrigerants that can be used to replace the CFC
and HCFC refrigerants. Currently R134a is the most commonly used new refrigerant. The various
refrigerants have different characteristics, which make them suitable for a particular application.

Following links provide more useful information on refrigerants -


Refrigerant Analysis

A periodic refrigerant analysis is important to detect and control contaminants in the refrigerant, which
can result in degradation / failure of the various components, and cause inefficient operation of the
unit. A log of the periodic refrigerant analysis should be maintained for trending. Refrigerants should be
tested for the following contaminants –

  • Moisture
  • Acid
  • Particulate/solids
  • Organic matter – sludge, wax, tars
  • Non-condensable gases

Moisture -

Moisture is one of the primary causes of contamination-related problems in a refrigeration system. It also
results in formation of some of the other contaminants mentioned above, which in turn cause further
damage to the chiller or DX unit. Presence of moisture results in following undesirable effects:

  • Ice formation in evaporator, expansion valve or orifice.
  • Degradation of lubricating oil due to hydrolysis.
  • Acid formation due to hydrolysis of refrigerant in the presence of moisture and  high temperature.
  • Corrosion of metals.
  • Copper plating

The copper plating phenomenon essentially involves carryover of copper ions from exchanger tubes to
the steel surfaces. Although the exact mechanism is not completely understood, it involves the following
three steps, 1) oxidation of the copper due to contaminants such as air, moisture & acid, 2)
solubilization and transport of copper ions by the lubricant, 3) deposition of the copper on hot clean
steel surfaces such as bearings. Excessive copper plating can result in a compressor failure. Typically
copper plating is a concern in systems with high level of contaminants and high bearing temperatures.

The most common causes for high moisture in the system are:

  • Water leakage in a chiller evaporator, or water cooled condenser.
  • Low pressure side leak resulting in entrance of air carrying moisture (typical problem in negative
    pressure machines)
  • Improper service procedures, i.e. system left open to atmosphere.

In case of moisture introduction due to improper service procedures, the dryer will eventually reduce
the moisture content resulting in a decreasing trend. If the trend is not decreasing then the likely
reasons are the first two causes, which require shutting down the chiller for repair. If the chiller cannot
be shutdown, it may be possible to temporarily provide on-line cleaning of the refrigerant to maintain
the moisture within acceptable limits, depending on the size of the leak. Online cleaning is similar to a
kidney function using a portable cleanup unit.

Moisture is normally absorbed in the refrigerant or lubricant, but free-water can also be present. The
solubility of water varies with different refrigerants. Generally, lower is the solubility of water in the
refrigerant, greater is the potential of free water being present, and lower is the acceptable level of
moisture in the system. Water concentration above the maximum solubility level will result in free-water.
The maximum water solubility level is different for liquid and vapor phase of the refrigerant, i.e.,
completely soluble water in liquid phase may transform into free-water in the vapor phase or vice versa
depending on the change in solubility from one phase to the other.

The acceptable levels of moisture in new or reclaimed refrigerants are given in ARI 700. These levels are
generally more demanding than what is typically feasible and acceptable in an operating system. There is
no experimental data available on the maximum permissible moisture levels in an operating system since
it is a function of several factors, but ASHRAE has some data on typical levels in a normally operating
system. The table below gives a comparison of ARI 700 allowable level and the level typically found in
normally operating equipment.

      Refrigerant                Allowable Moisture                Normal Operating Moisture Levels
                                        Level per ARI 700                   (ppm by wt) (Ref. ASHRAE)
      
                                        (ppm by wt)                                                                        
      
      R11                                        20                                     0 - 30 (centrifugal chillers
      
      R12                                        10                                     0 - 25 (centrifugal chillers)

      R22                                        10                                     0 - 56 (Recip & Screw chillers)

      R113                                      20                                     0 - 30* (similar to R11)

      R114                                      10                                     0 - 25* (similar to R12)

      R134a                                    10                                     0 - 25* (similar to R12)

      R500                                      10                                     0 - 25* (similar to R12)                              


* R113, R114, R134a, R500 data are not available in ASHRAE. Above data is based on similarity with the
other refrigerants (R500 is an azeotrope of R12 & R152a).

Testing method for moisture is specified in ARI 700. Based on above discussion and operating
experience, the
acceptance criteria for moisture should be as follows:

      Refrigerant                Normal                      Alert                        Fault
      
                                  ppm by wt                ppm by wt               ppm by wt

      R11                                0 - 20                       20 - 30                     >30       

      R12                                0 - 20                       20 - 25                     >25  

      R22                                0 - 30                       30 - 40                     >40

      R113                              0 - 20                        20 - 30                    >30

      R114                              0 - 20                        20 - 25                    >25

      R134a                            0 - 20                        20 - 25                    >25

      R500                              0 - 20                        20 - 25                    >25                  


Alert Level Actions
  • Increase frequency of sampling refrigerant to 2x
  • Sample lubricating oil with next sample of refrigerant to check for any signs of degradation
  • Check all potential causes of high moisture, and fix as required.
  • Check moisture indicators rigorously.
  • Check for any signs of lubricating oil degradation
  • Change filter dryers/desiccants as required

Fault Level Actions
  • Re-sample refrigerant to verify results
  • Recycle and clean refrigerant on line
  • Change all filter dryers/desiccants.
  • If trend continues, schedule a shutdown of the chiller and fix leaks.

Acids

A refrigeration system can contain two types of acids, organic and inorganic, depending on the type of
refrigerant and oil being used. Organic acids (such as oleic acid) are formed as a result of decomposition
of oil at high temperature in the presence of air as the oxidizing agent. These acids are slow to react,
soluble in oil, do not vaporize, and typically found in relatively small quantities in the oil sump. Inorganic
acids (such as hydrochloric acid and hydrofluoric acid) are formed as a result of decomposition of
refrigerants at high temperature in the presence of moisture. These acids are highly reactive, soluble in
water, vaporize, and typically found to be the dominant acids that may be present. Therefore, inorganic
acids are the real problem in a refrigerant system, which results in degradation of the equipment
internals. The major contributors to acid formation in a system are the presence of moisture and
abnormally high temperatures around the compressor i.e. bearings, motor windings, terminations,
compressor discharge etc. The presence of acids is specially hazardous in case of semi-hermetic and
hermetic compressors, since the acid vapor in refrigerant goes over motor windings and can eventually
lead to motor burnout. Therefore the amount of acids in a system should be kept to an absolute
minimum, and ARI 700 specifications should be followed strictly, i.e., maximum allowable limit for acid in
all refrigerants should be 1 ppm by weight.
The acids in a refrigeration system can be kept to a minimum by keeping the refrigerant dry and
preventing abnormally high temperatures in the system. Desiccant used in a filter dryer may be capable
of removing the acids, but the capacity and efficiency depends on several factors and is difficult to
determine.

Testing method for acids is as specified in ARI 700. Based on above discussion and operating experience,
the
acceptance criteria for acid should be as follows:

      Refrigerant                Normal                        Alert                         Fault
     
                                   ppm by wt                  ppm by wt                ppm by wt

             All                        0 - 0.8                        0.8 - 1.0                      >10                        

Alert Level Actions
  • Increase frequency of sampling refrigerant to 2x
  • Check all potential causes of high acid, and fix as required.
  • Change filter dryers/desiccants as required.

Fault Level Actions
  • Re-sample refrigerant to verify results
  • Recycle and clean refrigerant on line until acid concentration drops to acceptable level.
  • Change all filter dryers and desiccants.

Particulate/solids -

The solid contaminants can include metallic particles, chemical compounds or just dirt. The solids found
in a system normally result from wear, corrosion and chemical breakdown of the internals, or material left
in the system during servicing. The solid contaminants can create problems such as scoring compressor
cylinder walls and bearings, damaging motor insulation, plugging lubrication holes, plugging filter/dryers,
plugging expansion valves etc. The solid contaminants are removed to a great extent by the filter dryer,
but it needs to be sized to handle it without adding too much pressure drop in the system.
Testing method for particulate/solids, and the acceptance criteria should be as specified in ARI 700 for all
refrigerants. Any visual presence of dirt, rust or other particulate contamination should be reported as
alert condition.
If particulate/solids are found, the refrigerant filter should be replaced. If the problem persists in-spite
of changing the filter several times, on-line cleaning of the refrigerant may be required.
Note: Some labs will only give a pass or fail result of this test. If particulate/solids are found, it may be
necessary to have the lab give additional details such as size, quantity, color and particle type to provide
a better clue on the source.  

Organic matter – sludge, wax, tars

Organic contaminants are typically due to decomposition/degradation of organic materials in the system
such as oil, insulation, varnish, gaskets etc. These can circulate in the system and plug small orifices.
Organic contaminants dissolved in the liquid refrigerant may precipitate at lower temperature in the
expansion device, resulting in plugged capillary tubes or sticky expansion valves. Organic contaminants
can also coat heat transfer surfaces resulting in cooling inefficiency. Since heat degrades most organic
materials, operating conditions with excessively high temperatures should be avoided. If an organic
contaminant is dissolved in the liquid refrigerant, it may not be removed by the filter-dryer.
Testing method for organic matter is specified in ARI 700 for High Boiling Residue test.
ARI specifies 0.01% by volume of high boiling residue for most new or recycled refrigerants. However, this
is not practical for operating machines due to miscibility of lubricating oils in refrigerants, i.e. oil
carryover. Based on operating experience, the
acceptance criteria for organic matter should be as
follows:

      Refrigerant                       Normal                         Alert                         Fault
      
                                        % by Vol.                      % by Vol.                   % by Vol.

            All                                0 - 0.1                         0.1 - 0.2                     >0.2       


Alert Level Actions
  • Increase frequency of sampling refrigerant to 2x
  • Change refrigerant filters as required.

Fault Level Actions
  • Re-sample refrigerant to verify results
  • Recycle and clean refrigerant on line till levels drop to acceptable levels.
  • Change all refrigerant filters.

Non-condensable Gases -

Non-condensable gases are chemically inert gases, which do not liquefy in the condenser. This
contaminant typically results from incomplete evacuation, low side air in-leakage, chemical reactions &
decomposition of materials at high temperature.  Typically the first two causes are the primary reasons
for high non-condensable gases. These gases reduce cooling efficiency, cause high starting and running
currents, and result in higher than normal compressor discharge pressure & temperature, which speeds
up undesirable chemical reactions.
Testing method for non-condensable gases is specified in ARI 700.
The quantity of non-condensable gases that is harmful depends on the design and size of the
refrigeration unit and the nature of the refrigerant. ARI 700 specifies a limit of 1.5% of non-condensable
gases by volume for most new or recycled refrigerants, which is unrealistic to maintain continuously in an
operating system, especially the negative pressure machines. Based on operating experience, the
acceptance criteria for non-condensable gases should be as follows:

              Refrigerant                        Normal                       Alert                        Fault
                                                        % by Vol.                   % by Vol.                % by Vol.

                All                                     0 - 5                          5 - 10                        >10

Alert Level Actions
  • Review operating parameters to confirm high non-condensable gases.
  • Increase frequency of sampling refrigerant to 2x
  • Check purge unit/dehydrator for proper operation
  • Increase purge rate. Caution should be observed to avoid excessive loss of refrigerant due to purge
    unit inefficiency.

Fault Level Actions
  • Re-sample refrigerant to verify results
  • If acceptable levels are not achieved, shutdown the machine and repair the leaks or faulty purge
    operation, as applicable.
  • If the machine cannot be shutdown, recycle and clean refrigerant on line until it reaches
    acceptable level.

Oil Analysis

The oil analysis provides a “look inside” a compressor without disassembly. When unacceptable wear
conditions develop inside the compressor, a corresponding detectable change in the characteristics of
the oil will become evident. The results from oil analysis should be used in conjunction with vibration
analysis and bearing temperatures to detect excessive bearing wear. A log of the periodic oil analysis
should be maintained to provide the trend.

The oil sample should be tested for the following properties:
  • Metal wear
  • Moisture
  • Acidity
  • Viscosity
  • Solid residue